Eight-legged spider robot

The problem

Wheels perform brilliantly on asphalt but fail on sand and rubble. Places like Jordan's Badia and post-earthquake debris sites need a way to move that doesn't require a flat surface. Walking on legs is the natural answer, but legged robots usually need a motor per joint and complex calculations. The Theo Jansen mechanism gives a near-natural gait with one motor and purely mechanical joints, achieving a comparable result at a fraction of the cost and complexity.

How it works

1. RotationTwo geared motors on each side of the frame produce the rotation.
2. TransportA set of gears transfers the rotation and distributes it to the two groups of legs.
3. ConversionJansen linkages convert the rotation into an elliptical path that mimics a footstep.
4. SynchronizationOpposite phases between the groups keep four legs on the ground at all times.
5. GuidanceDifferent speeds on the two motors turn the robot left or right.
6. ControlA wireless receiver converts the remote's commands into speeds for the two motors.

Project features

• A visually striking mechanical project: the motion itself grabs the defense committee's attention.
• It demonstrates understanding of kinematics and mechanical linkages, not just programming.
• It walks on sand and gravel where wheels get stuck — a result that can be tested in front of the committee.
• It can be extended with a camera or distance sensors to avoid obstacles.
• The mechanism is well known and open source, so references are available and the result is assured.

Expected challenges

These are the main obstacles to expect during the build, laid out clearly so you know them before you start.

• Precision in cutting the linkages: a one-millimeter error in a link's length ruins the whole gait.
• Joint clearance: too tight blocks movement, too loose causes wobbling.
• Weight distribution: the battery and board must be near the center, or the robot tips over.
• Motor torque: the robot stalls under its load if torque is lower than needed.
• At startup the robot draws far more current than expected.

The consultation gives you a solution for each one.

Expected committee questions

Prepare your answers in advance: these questions come up often in defenses of similar projects.

1. Why was the Theo Jansen mechanism chosen over servo-driven legs with a motor per joint?
2. How were the linkage lengths calculated, and how does an error in them affect the gait?
3. How are eight legs synchronized with only two motors?
4. What's the steepest slope or largest obstacle the robot can handle, and how was it tested?

Practice the defense, question by question